Household mould may cause people with asthma to develop severe forms of the disease, a study suggests.

Researchers in France have found a strong link between people who are sensitive to the type of mould that can sometimes be found on plants and paintwork in the home, and those who have life-threatening asthma attacks.

They believe mould, more than any other allergens, including dust mites or cats, may be responsible for triggering severe asthma.

This report could be a very important study for people with asthma

Professor Martyn Partridge, National Asthma Campaign

The researchers said their findings highlighted the need for people with the disease to ensure their homes were mould-free and were well ventilated.

Dr Mahmoud Zureik and colleagues at the National Institute of Health and Medical Research in Paris examined more than 1,100 adults with asthma.

The participants are involved in the European Community Respiratory Health Survey, which is examining increased rates of asthma in people in Europe, Australia and the United States.

Sensitive to allergens

Each of the participants was tested to gauge whether their asthma symptoms got worse when exposed to a variety of allergens.

These included household mould, dust mites, a type of grass and cats.

The study found that three out of four people were sensitive to at least one allergen, with grass and dust mites topping the list.

Two out of three people were sensitive to two or more allergens.

Almost one in five was allergic to a plant fungus or mould that typically grows on dead plants, damp walls or paintwork and old food.

Those who were sensitive to these moulds were much more likely to have a severe form of asthma. There was not a similar link with pollens or cats.

'Pay attention'

Writing in the British Medical Journal, the authors suggested this may be because mould spores are much smaller and can reach the lower airways where they can cause most damage.

In addition, these spores were present in the home where people generally spent most of their time.

The authors called on doctors to tell patients about the risks.

"Those people with asthma who are sensitised to airborne moulds should be educated to pay careful attention to symptoms and comply with treatment," they said.

"Patients should be encouraged to decrease exposure by avoiding indoor conditions that facilitate the growth of moulds - for example, by better ventilation and by decreasing dampness."

"This report could be a very important study for people with asthma. What has been demonstrated is an 'association' between mould sensitisation and severe asthma.

"We cannot be certain that this is a cause and effect relationship but it might be."

"What is now needed is an intervention study and this would need to be in two parts; firstly looking to see if a reduced exposure to moulds prevented those with asthma moving into the severe category, and secondly seeing if reducing exposure to moulds by those with severe asthma improves control of the disease."